The present invention relates to a gumming device and to a method for gumming a web of wrapping material.
The invention is applicable, to advantage, for the purpose of automatically emptying and/or cleaning devices by which adhesive is deposited on a web of wrapping material in manufacturing machines used in the tobacco industry, the field to which reference is made explicitly in the following specification albeit with no limitation in scope implied.
More exactly, the present invention relates to a roller type gumming device utilized in a filter tip attachment machine for applying a layer of adhesive to a continuous strip of paper that is then divided up into discrete lengths, or tipping papers, by means of which single filters are joined ultimately to relative cigarette sticks.
Conventionally, a layer of adhesive is applied to the continuous strip or web of paper using a gumming device that comprises a pair of rollers disposed side by side and counter-rotating about horizontal axes, which are urged resiliently one against the other along an area of mutual contact. One of the rollers is a transfer roller, whilst the other is a gumming roller of which the surface revolves tangentially to the continuous strip.
The transfer roller and the gumming roller combine to form a trough, created between mutually opposed portions of the respective cylindrical surfaces located immediately above the area of mutual contact. The space above the trough is occupied by the outlet nozzle of a pipeline connected to a tank containing a supply of adhesive.
Adhesive directed into the trough, which extends the full length of the straight line generator of contact between the two rollers, forms a pool from which to prime the gumming roller.
The direction of rotation induced in the gumming roller is such that a layer of adhesive formed on the cylindrical surface beyond the area of contact with the transfer roller will be transferred in turn to the continuous strip. The depth of the layer of adhesive is regulated by the pressure created along the area of contact between the two rollers.
The adhesive consists normally in a vinyl based product, and the more its chemical and physical properties (temperature, viscosity, bonding power, etc.) can be maintained constant, the more effective and efficient the gumming process will be. With the adhesive properly conditioned, it can be distributed uniformly by the gumming device on the continuous strip. This will happen, in practice, as long as there is always fresh adhesive in the trough above the area of mutual contact between the two rollers of the gumming device.
In reality, given the heat generated by the filter attachment machine during operation, and the pressure generated between the rollers, the temperature of the adhesive occupying the trough will rise, and this tends to degrade the chemical and physical properties of the adhesive.
It has been found, in effect, that under normal operating conditions, the roller type gumming device is unable to keep the adhesive in a suitably fluid state, due to the partial drying effect induced and the consequent formation of lumps. This is a problem that occurs, in particular, during stoppages: in these situations, the web of paper material is distanced from the gumming roller and the delivery of adhesive from the tank suspended, with the result that the pool of adhesive held between the rollers will tend to degrade through stagnation, and must be removed.
This removal operation is performed manually by persons tasked with the job of cleaning the machine, and the additional work involved results in higher servicing costs.
The object of the present invention is to provide a gumming method and a relative device that will be unaffected by the drawbacks mentioned above.